Compression

[Glwack]

What should the compression be for a 1981 Johnson 4.5 hp? Carb is rebuilt good spark just pops won't start

 

[oldboat1]

Idle mix needle should be open about 1 1/2 turns initially. 80 or 90 compression would work.

 

[Glwack]

Compression is 60 both cyinders. Moyer has been sitting for 8 years. I have sprayed wd40 let soak, wd40 rust breaker let soak, 10 weight oil let soak. Has brought compression from 50 to 60. But all. It will pop and sounds like it is in the leg. Any other suggestions ?

 

[Glwack]

Compression is 60 both cyinders. Moter has been sitting for 8 years. I have sprayed wd40 let soak, wd40 rust breaker let soak, 10 weight oil let soak. Has brought compression from 50 to 60. But all. It will pop and sounds like it is in the leg. Any other suggestions ?

 

[boobie]

Will your spark jump a 1/4" open air gap on a spark tester.??

 

[racerone]

Plug wires reversed ?

 

[Crosbyman]

were all carb passages flushed out with cleaner and blown dry with high pressure air
are you using fresh gas mix ?

 

[Glwack]

Spark jumps 1/2 inch plug wires correct and carb rebuilt by pro boat shop.

 

[Sea Rider]

If all electrical parts are working spot on, an outboard showing very low compression numbers will be extremely difficult to start. Seems a candidate for next piston and ring size from standard ones.. Compression should be min 100 PSI to start well as it should.

Happy Boating

 

[Crosbyman]

GIwack…. ​

sea rider..

imho several of my oldies work fine below 80 the MQ series (9.5hp) works fine at 65-70 the 4.5 motor may not have a lot of power but with sucking in some fuel fix and igniting it should produce some… revolutions

that said, it is a simple carb to take apart and clean… again if need be . all it takes is a spec of dirt to kill a carb


Pro sop or not they should have tested that engine after the carb job they charged good $$ for, if only to check their work and inform the customer of any no-go situation requiering additional work (electricals ??)

we do not know if the inlet needle is stuck, LS & HS orifices plugged,,, fuel filter new ? ,,, gas mix fresh ?? ​

some 8 year old tank varnish could have floated around and down

1- if possible ask the pro-shop why the carb job did not produce a working motor ??? assuming it was cleaned recently

2- take the carb apart and reclean test the inlet needle (blow test ...air in when held UP no air in held upside down )

see links on older carb model…. same cleaning principle

http://www.outboard-boat-motor-repair.com/Evinrude 3 HP Lightwin Outboard Boat M otor/Evinrude%20Johnson%203%20HP%201952-1967%20Carburetor%20Tune-UP.htm
https://maxrules.com/fixtuneitup2.html

https://maxrules.com/fixtuneitup2.html

 

[Glwack]

I is this site to get the rings and Pistons? I use to work on Mercury years ago. Raced hydroplanes never worked on OMC. Do they have reed valves?

 

[Glwack]

I is this site to get the rings and Pistons? I use to work on Mercury years ago. Raced hydroplanes never worked on OMC. Do they have reed valves? Looks like a new motor and would like to get it running.

 

[Crosbyman]

try the easy stuff first before getting $$$$ parts for it ….. just mho

 

[Glwack]

I have done all the easy stuff, I guess I need to into it. I need a good source for parts. I failed to says that I removed the carb and sent it off to rebuild.